Add Gitea workflow publishing the library to the public Maven registry

- .gitea/workflows/publish.yml: build, test and deploy on push to main
  (snapshot), on v* tags (release version from the tag) and manually;
  authenticates with the REGISTRY_TOKEN secret
- demo app is excluded from deployment
- pin maven-deploy-plugin and versions-maven-plugin
- README: how to consume the package

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G71TQ5jDETVwdUJxGAwaiT

.gitea/workflows/publish.yml

@@ -0,0 +1,46 @@
+# Builds, tests and publishes the library modules (parent, core, autoconfigure, starter) to the Gitea Maven
+# registry of the "public" owner. The demo app is not published.
+#
+#   push to main        -> <version>-SNAPSHOT from pom.xml
+#   tag v1.2.3          -> release 1.2.3
+#   manual run          -> whatever pom.xml says
+#
+# Needs the repository/organization secret REGISTRY_TOKEN: a Gitea access token with "write:package" scope.
+name: Publish
+
+on:
+  push:
+    branches: [main]
+    tags: ['v*']
+  workflow_dispatch:
+
+env:
+  REGISTRY_URL: ${{ gitea.server_url }}/api/packages/public/maven
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: '27'
+          cache: maven
+          # writes ~/.m2/settings.xml with a <server id="gitea"> reading these env vars
+          server-id: gitea
+          server-username: REGISTRY_USERNAME
+          server-password: REGISTRY_TOKEN
+
+      - name: Set release version from tag
+        if: startsWith(gitea.ref, 'refs/tags/v')
+        run: mvn -B -ntp versions:set -DnewVersion="${GITEA_REF_NAME#v}" -DgenerateBackupPoms=false
+        env:
+          GITEA_REF_NAME: ${{ gitea.ref_name }}
+
+      - name: Build, test and publish
+        run: mvn -B -ntp deploy -DaltDeploymentRepository="gitea::${REGISTRY_URL}"
+        env:
+          REGISTRY_USERNAME: ${{ gitea.actor }}
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}